Optical fiber connectors and splices (hereinafter referred to collectively as "connectors") are an essential part of substantially any optical fiber communication system. For instance, connectors may be used to join segments of fiber into longer lengths, or to connect fiber to active devices such as radiation sources, detectors, or repeaters, or to passive devices such as switches or attenuators.
The task of an optical fiber connector is twofold. First, it must couple or join two optical fibers with minimum insertion loss. Second, it must provide mechanical stability and protection to the junction in its working environment. Achieving low insertion loss in coupling two fibers is generally a function of the alignment of the fiber ends, the width of the gap between the ends, and the optical surface condition of the ends. Stability and junction protection is generally a function of connector design, e.g., minimization of differential thermal expansion effects.
The prior art knows many approaches to achieving fiber alignment. Among them are V-grooves, three-rod containment, resilient ferrules, elastomeric bushings, jewel bushings, conical nose/conical bushing, and precision ferrule/precision bushing devices. A discussion of some prior art connectors can be found, for instance, in R. Schultz, Proceedings of the Optical Fiber Conference, Los Angeles (September 1982), pp. 165-170.
Prior art optical fiber connectors often contain one or more precision-machined parts and are therefore relatively costly items. Whereas this may be acceptable for some applications, e.g., in trunk lines, in other cases the bost of such prior art connectors might constitute a significant fraction of the total installation cost. Thus, strong incentives exist for devising optical fiber connectors that do not require expensive precision-machined parts.
A further and very important consideration in connector design is the relative ease of field installation of the connector, since a complicated and lengthy installation procedure may significantly affect the installed cost of a multiconnector optical fiber network. It is thus desirable that installation of a connector not only be accomplishable within a relatively short period of time, but also that the installation not require special skills or manipulations not easily carried out in the field.
Ideally, an optical fiber connector would be a low-cost item not comprising precision-machined parts, be easily and quickly installable in the field in a process that requires participation of only one installer, that does not require the use of special alignment or detection equipment, that yields connections of very low loss that are insensitive to environmental effects such as temperature changes, and that is rugged and usable in a variety of environments. To the best of our knowledge, no connector exists that meets this wish list.
A prior art connector that does not use precision-machined parts and which has many of the abovelisted desirable features is disclosed in coassigned U.S. patent application Ser. No. 527,341, incorporated herein by reference. This prior art connector uses two drawn glass tubular plugs, with the fiber inserted into the bore of the plug, and the connection between the two fiber ends made by inserting the plugs in end-to-end fashion into an alignment sleeve that maintains the outer surfaces of the two plugs in registry. This connector design relies on the fact that the plugs can be produced to very close tolerances by drawing from a glass preform.
A further prior art connector that has many of the above-listed desirable characteristics is disclosed in coassigned U.S. Pat. No. 4,545,644 also incorporated herein by reference. That application discloses an optical fiber connector comprising two cylindrical plugs with axial bores into which the respective fiber ends are inserted, with the plugs then inserted into a housing. The housing comprises a multiplicity, typically three, of basically cylindrical alignment rods, and means for maintaining the alignment rods in contacting relationship with both plugs. A simple spring clip is an example of such means. At least one of the alignment rods carries a "flat", i.e., a region, extending from one of the ends of the rod towards the middle, where a small amount of rod material has been removed such as to create a small offset. One or more flat-carrying alignment rods can be used to deliberately introduce an eccentricity into the plug alignment, yielding the potential to eliminate, by rotation of one plug with respect to the other, any misalignment between the fiber cores that is due to such unavoidable eccentricities as that of the fiber core with respect to the fiber surface, of the fiber with respect to the bore of the plug, or of the bore of the plug with respect to the plug cylinder surface.
In this application we are also disclosing a connector which has many of the above-listed desirable characteristics. In particular, the inventive connector does not contain precision-machined parts, can be quickly and easily installed by one installer without requiring the assistance of further personnel in the central office, and without the need for special tools or alignment fixtures, and, in many cases, even without the use of local detection apparatus, and is temperature stable and versatile. Furthermore, the connector can consistently yield low-loss connections and, if desired, can be fine tuned to produce very low-loss connections in single mode fiber, of the order of 0.1 dB or less.